Do Nortech do a full kit? I can only see a tubular manifold for a Golf R.
Can you weld and do you have stainless tube cutting equipment? Making a DP is easy if you have the kit, especially with V band flanges. I would route the wastegate dump back into the DP rather than a silly 'race car' screamer pipe. The noise will quickly piss you off and exhaust gas will get into the cabin, not to mention being illegal. And we all know Carbon monoxide is the silent killer.
You don't need a fancy tig welder, but back purging is a good idea to prevent 'sugaring', which can break off and chip turbine wheels. I made a DP for my VR6 turbo years ago with a cheap MIG welder from Machine mart, a hacksaw, some patience and a lot of coffee
Have a look on Youtube for 'Project MK5' on Deutsche Auto Parts' channel. They built a big turbo car and one of the episodes goes over making a DP, if you want some inspiration.